It is known that a radio access network allows a plurality of users provided with respective radio terminals (e.g. mobile phones, PDAs, laptop PCs, etc.) to access a number of telephone services and/or data services (such as Internet access, text message services and multimedia message services, e-mail, etc.). Exemplary radio access networks are the GSM (Global System for Mobile communications), the UMTS (Universal Mobile Telecommunications System) and the WiMAX (Worldwide Interoperability for Microwave Access).
A radio access network typically comprises a plurality of network nodes (or simply nodes), wherein each node comprises one or more access devices. Each access device has a coverage area and it is capable of exchanging traffic via radio with radio terminals located within its coverage area. For instance, in a GSM radio access network the access devices are called BTS (Base Station Transceiver).
Typically, the nodes of a radio access network are connected to one another according to a tree logical topology, wherein each terminal node is connected to an upstream node and wherein each intermediate node is connected to at least one downstream node and to one upstream node. Each node is connected to adjacent nodes (both downstream and upstream) either by means of wireless transceivers (e.g. microwave transceivers) or by means of wired transceivers. The root of the tree logical topology corresponds to a traffic collection center. For instance, in a GSM radio access network the traffic collection center is termed BSC (Base Station Controller).
A radio access network is typically configured to transport a plurality of traffic flows across the tree logical topology. In the following description and in the claims, the expression “upstream traffic flow” or simply “upstream flow” will designate a traffic flow transported from a node to the traffic collection center. Besides, the expression “downstream traffic flow” or simply “downstream flow” will designate a traffic flow transported from the traffic collection center to a node.
In particular, the transceivers connecting each node of a radio access network to the adjacent nodes are typically configured to transmit and receive TDM (Time Division Multiplexing) traffic flows which may be either synchronous (e.g. SDH or Sonet tributaries) or plesiochronous (e.g. PDH tributaries).
By assuming that a terminal node comprises n access devices (wherein n≥1), the terminal node typically receives through each of the n access devices an upstream flow comprising traffic transmitted by radio terminals located within its coverage area. Therefore, the terminal node typically performs a TDM multiplexing of the n received upstream flows, and it transmits the n multiplexed upstream flows to the intermediate node located immediately upstream.
By assuming that the intermediate node is connected only to the terminal node, and that it further comprises m access devices (wherein m≥1), the intermediate node receives the n multiplexed upstream flows from the terminal node. Further, typically, the intermediate node receives through each of the m access devices an upstream flow comprising traffic transmitted by radio terminals located within its coverage area. Therefore, the intermediate node typically performs a TDM multiplexing of the n+m received upstream flows, and it transmits the n+m multiplexed upstream flows to the intermediate node located immediately upstream.
Each node (both the terminal node and the intermediate node) performs TDM multiplexing of the received upstream flows by means of a respective TDM matrix. In particular, the TDM matrix switches each upstream flow received through one of its inputs towards one of its outputs. The output towards which each upstream flow has to be switched is determined by means of a routing table. The routing table typically associates each input of the TDM matrix to an output of the TDM matrix. Since the radio access network has a tree logical topology, the TDM matrix typically has a single output towards which all the upstream flows are transmitted in the upstream direction. Accordingly, in the routing table all the inputs of the TDM matrix are associated to a same output.